Optical detectors and methods of using them

ABSTRACT

Certain embodiments described herein are directed to optical detector and optical systems. In some examples, the optical detector can include a plurality of dynodes, in which one or more of the dynodes are coupled to an electrometer. In other configurations, each dynode can be coupled to a respective electrometer. Methods using the optical detectors are also described.

PRIORITY APPLICATIONS

This application claims priority to each of U.S. Patent Application No.61/728,188 filed on Nov. 19, 2012, to U.S. Patent Application No.61/732,865 filed on Dec. 3, 2012 and to U.S. Patent Application No.61/781,945 filed on Mar. 14, 2013, the entire disclosure of each ofwhich is hereby incorporated herein by reference for all purposes.

TECHNOLOGICAL FIELD

Certain features, aspects and embodiments are directed to opticaldetectors and methods of using them. In some instances, the opticaldetector can be configured to amplify a light signal using a pluralityof dynodes.

BACKGROUND

Light emission from species is often detected using a photomultipliertube. The photomultiplier tube is designed to amplify the light signalto permit detection of the light.

SUMMARY

Certain aspects described herein are directed to detectors that canreceive photons, measure signals from analog dynode stages and can shuntor shut down dynodes downstream of a saturated dynode to protect thedynodes of the detector. In some configurations, the detector isconfigured to function without any pulse counting, e.g., comprises onlyanalog stages and no pulse counting stage or pulse counting electrode,and may measure a plurality of analog signals, scale each signal andaverage the signals. By measuring the input or output current tomultiple dynodes, and shutting down high current dynodes, the dynamicrange of the detector can be extended and linearity can be improved.

In a first aspect, an optical system configured to receive photons, theoptical system comprising a photocathode, an anode and a plurality ofdynodes, between the photocathode and the anode is provided. In someembodiments, each dynode is configured to amplify a signal from thephotons received by the photocathode. In certain instances, each of theplurality of dynodes is electrically coupled to a respectiveelectrometer.

In certain embodiments, the system can further comprise a firstprocessor electrically coupled to each electrometer. In someembodiments, the first processor is configured to measure the input oroutput current into each respective dynode. In certain examples, thefirst processor is configured to calculate a mean input current usingreceived input current signals and using the gain of the respectivedynode. In other examples, the first processor is configured tocalculate a gain between consecutive dynodes by comparing a current,e.g., input or output current, of the first dynode to a current, e.g.,input or output current, of a dynode immediately upstream of the firstdynode. In some embodiments, each electrometer is electrically coupledto a signal converter, e.g., an analog-to-digital converter or an ionpulse counter or other suitable signal converters. In some embodiments,a respective power converter can be electrically coupled to eachelectrometer and analog-to-digital converter pair. In some instances,the first processor is configured to measure all dynode currentssimultaneously. In other embodiments, the first processor (or thedetector) is configured to prevent a current overload at each dynode. Inadditional examples, the first processor (or detector or both) isconfigured to alter the voltage at a saturated dynode (relative to aprevious, upstream dynode) to reduce its electron gain to the previousdynode and/or reduce the ion current for all downstream dynodes. Infurther examples, the processor (or detector or both) is configured toinvert the polarity of the voltage to the previous dynode or asubsequent dynode or both. In other examples, the processor (or detectoror both) is configured to prevent any substantial secondary electronemission to a downstream dynode adjacent to the dynode where thesaturation current is detected. In some embodiments, voltage of theoptical detector is not adjusted between measurements. In additionalembodiments, the gain of the optical detector is constant. In someexamples, gain of the optical detector is not user adjustable. In otherembodiments, the optical detector is configured to provide independentvoltage control at each dynode of the plurality of dynodes. In someexamples, dynode to dynode voltage is regulated to keep the voltagesubstantially constant (or constant) while allowing the input or outputcurrents to vary at each dynode. In further examples, dynamic range ofthe current measurements is greater than 10¹⁰ when measuring the currentat a rate of 100 kHz. In other examples, the signal from everyelectrometer is used by the processor to calculate a mean input current.In some embodiments, the processor is configured to calculate the meaninput current by calculating the input currents of the dynode signalswhich are above a minimum noise threshold, e.g., above a noise currentsignal, and below a maximum saturation threshold, e.g., below asaturation current signal. In additional embodiments, the processor isconfigured to scale each non-discarded calculated input currents using arespective gain and average the scaled input currents to provide themean input current. In further embodiments, the system can include atleast one optical element optically coupled to the photocathode. In someinstances, an entry slit width of the optical detector (and if desiredthe exit slit width) remains constant when measuring samples havingdifferent concentrations. In other embodiments, entry slit width (and ifdesired the exit slit width) of the optical detector is not adjustable.

In another aspect, an optical system configured to receive an opticalemission from a sample, the optical system comprising a photocathode, ananode and a plurality of dynodes between the photocathode and the anodeis provided. In some configurations, the system comprises multiplesections of continuous dynodes, e.g., where each section comprises aplurality of dynodes. In some arrangements, at least one section of theplurality of dynodes is electrically coupled to an electrometer.

In certain embodiments, the system further comprises at least oneadditional electrometer electrically coupled to one of the plurality ofdynodes. In some embodiments, the system further comprises a firstprocessor electrically coupled to each electrometer and configured tomeasure the input or output current into each respective dynode. Inother embodiments, at least one dynode without a respective electrometeris positioned between dynodes that are electrically coupled to anelectrometer. In further embodiments, one or more sections comprise aplurality of electrometers, in which every other dynode is electricallycoupled to an electrometer. In some examples, one or more sectionscomprise a plurality of electrometers, in which every third dynode iselectrically coupled to an electrometer. In other examples, the systemcan comprise a plurality of electrometers, in which every fourth dynodeis electrically coupled to an electrometer. In yet other instances, oneor more sections can comprise a plurality of electrometers, in whichevery fifth dynode is electrically coupled to an electrometer. Infurther embodiments, each electrometer can be electrically coupled to asignal converter. In some examples, each electrometer is electricallycoupled to an analog-to-digital converter, an ion pulse counter or othersuitable converters to provide, for example, simultaneous digitalsignals to the processor from each of the dynodes electrically coupledto an electrometer. In some embodiments, the processor is configured toprovide a mean digital signal representative of the concentration of thesample using the simultaneous digital signals. In other embodiments, thesystem can include a processor electrically coupled to the plurality ofdynodes and configured to prevent a current overload at one or moredynodes or at each dynode, e.g., each dynode can be electricallyisolated from other dynodes to provide separate signals to theprocessor. In some instances, the first processor (or detector or both)is configured to alter the voltage at a saturated dynode (relative to aprevious dynode) to reduce its electron gain to the previous dynode andreduce the ion current for other downstream dynodes. In other examples,voltage of the optical detector is not adjusted between measuringoptical emissions from samples having different concentrations. Infurther examples, the gain of the optical detector is constant. In someembodiments, gain of the optical detector is not user adjustable. Inother embodiments, the processor is configured to provide independentvoltage control at each dynode of the plurality of dynodes. In someembodiments, dynode to dynode voltage is regulated to keep the voltagesubstantially constant (or constant). In other embodiments, dynamicrange of current measurement is greater than 10¹⁰ when measuring the ioncurrent at a rate of 100 kHz. In some embodiments, the signal from everyelectrometer is used by the processor to calculate a mean electronmultiplier input current. In certain embodiments, the processor isconfigured to calculate a mean input current by calculating the inputcurrents of dynode signals which are above a minimum noise threshold,e.g., above noise current signal, and below a maximum threshold, e.g.,below a saturation current signal. In some embodiments, the processor isconfigured to scale each non-discarded calculated input current using arespective dynode gain and average the scaled input currents to providea mean input current. In certain examples, the system can include atleast one optical element optically coupled to the photocathode. Inother examples, an entry slit width of the optical detector (and/or theexit slit width) remains constant when measuring samples havingdifferent concentrations. In some embodiments, entry slit width of theoptical detector (and/or exit slit width) is not adjustable.

In an additional aspect, an optical detector comprising a photocathode,an anode and a plurality of dynodes, between the photocathode and theanode, in which each of the plurality of dynodes is configured toelectrically couple to a respective electrometer is provided.

In certain embodiments, the plurality of dynodes and the electrometersare in the same housing. In some embodiments, each electrometer iselectrically coupled to a respective signal converter. In otherembodiments, each of the respective signal converters is ananalog-to-digital converter, an ion pulse counter or other signalconverters. In some embodiments, each of the signal converters isconfigured to provide a signal to a processor in an electricallyisolated manner. In other examples, the detector comprises a respectivepower converter electrically coupled to each electrometer andanalog-to-digital converter pair. In some configurations, for one ormore dynodes, e.g., each dynode, the electrometer and the converted canbe at substantially the same electrical potential, e.g., where theprocessor is at ground potential. In some examples, the detectorcomprises a processor electrically coupled to each of the plurality ofdynodes and configured to prevent a current overload at each dynode. Incertain embodiments, the processor is configured to alter the voltageat, upstream or downstream of a dynode where a saturation current isdetected. In some embodiments, the processor is configured to invert thepolarity of a voltage at, upstream or downstream of the dynode where thesaturation current is detected. In other embodiments, the processor isconfigured to prevent any substantial secondary electron emission to adownstream dynode adjacent to the dynode where a saturation current isdetected.

In another aspect, an optical detector comprising a photocathode, ananode and a plurality of dynodes, between the photocathode and theanode, in which each of the plurality of dynodes is electrically coupledto a respective electrometer configured to provide an output signal isprovided.

In certain embodiments, the plurality of dynodes and the electrometersare in the same housing. In other embodiments, each electrometer iselectrically coupled to a respective signal converter. In additionalembodiments, each of the respective signal converters is ananalog-to-digital converter, an ion pulse counter or other suitablesignal converters. In further embodiments, each of the analog-to-digitalconverters is configured to electrically couple to a processor in anelectrically isolated manner. In some examples, the optical detectorcomprises a respective power converter electrically coupled to eachelectrometer and analog-to-digital converter pair. In other embodiments,the detector comprises a processor electrically coupled to each of theplurality of dynodes and configured to prevent a current overload ateach dynode, e.g., each dynode can be electrically isolated from otherdynodes to provide a signal to the processor. In some embodiments, theprocessor is configured to alter the voltage at, upstream or downstreamof a dynode where a saturation current is detected. In some instances,the processor is configured to invert the polarity of a voltage at,upstream or downstream of the dynode where the saturation current isdetected. In other embodiments, the processor is configured to preventany substantial secondary electron emission to a downstream dynodeadjacent to the dynode where a saturation current is detected.

In an additional aspect, an optical detector comprising a signalamplification device constructed and arranged to receive photons emittedby a sample and to amplify a signal representative of the receivedphotons by secondary ejection of electrons from surfaces, in which thesurfaces that are effective to eject electrons to amplify the signal areeach configured to electrically couple to an electrometer is described.

In certain examples, at least two adjacent surfaces effective to ejectelectrons are configured to electrically couple to a respectiveelectrometer. In other examples, every other surface effective to ejectelectrons is configured to electrically couple to a respectiveelectrometer. In some embodiments, every third surface effective toeject electrons is configured to electrically couple to a respectiveelectrometer. In additional embodiments, the electrometer is configuredto electrically couple to a signal converter, e.g., an analog-to-digitalconverter, ion pulse counter or other suitable signal converter. Inother examples, the signal converter is an analog-to-digital converter.In some embodiments, the detector can include a power converterelectrically coupled to the electrometer and to the analog-to-digitalconverter. In certain examples, the detector can include a firstprocessor electrically coupled to each of the surfaces and configured toprevent a current overload at each surface, e.g., each surface can beelectrically isolated from other surfaces to provide a signal to theprocessor. In some embodiments, the processor is configured to measureall surface currents simultaneously. In certain embodiments, theprocessor is configured to alter the voltage at a saturated surface or asurface upstream or downstream of the saturated surface.

In another aspect, an optical detector comprising a signal amplificationdevice constructed and arranged to receive photons emitted by a sampleand to amplify a signal representative of the received photons bysecondary ejection of electrons from surfaces, in which at least onesurface that is to eject electrons to amplify the signal is electricallycoupled to an electrometer is provided.

In certain embodiments, at least two of the surfaces are electricallycoupled to a respective electrometer. In some embodiments, every surfaceis electrically coupled to a respective electrometer. In otherembodiments, every third surface is electrically coupled to a respectiveelectrometer. In additional embodiments, each electrometer iselectrically coupled to a signal converter, e.g., an analog-to-digitalconverter, an ion pulse counter or other signal converter. In someexamples, the signal converter is an analog-to-digital converter. Inother examples, the detector comprises a power converter electricallycoupled to each electrometer and analog-to-digital converter pair. Insome embodiments, the detector comprises a first processor electricallycoupled to each of the plurality of surfaces and configured to prevent acurrent overload at each surface, e.g., each surface is electricallyisolated from other surfaces. In certain examples, the processor isconfigured to measure all surface currents simultaneously. In certainembodiments, the processor is configured to alter the voltage at asaturated surface or a surface upstream or downstream of the saturatedsurface.

In an additional aspect, a method of detecting optical emissioncomprising simultaneously detecting a current signal, e.g., inputcurrent signal or output current signal, at each dynode of a pluralityof dynodes of a photomultiplier configured to receive photons, andaveraging the detected current signals at each dynode that comprises ameasured current signal above a noise current signal and below asaturation current signal to determine a mean current is disclosed.

In certain embodiments, the method can include terminating signalamplification at a dynode where a saturation current is measured. Insome embodiments, the method can include altering the voltage at adynode adjacent to the dynode where the saturation current is measuredto terminate the signal amplification. In some examples, the method caninclude determining the mean current by calculating the currents at alldynodes and discarding calculated currents below the noise currentsignal and above the saturation current signal, scaling eachnon-discarded calculated current by its respective gain, and averagingthe scaled currents to determine the mean current. In certain examples,the method comprises providing a floating voltage to each dynode of theplurality of dynodes. In other examples, the method comprisescontrolling the voltage at each dynode independently of voltage at theother dynodes of the plurality of dynodes. In further examples, themethod comprises measuring the photons without adjusting the gain. Insome embodiments, the method comprises measuring optical emission from aplurality of samples comprising different concentrations withoutadjusting the gain of the photomultiplier. In other embodiments, themethod comprises measuring optical emission from a plurality of samplescomprising different concentrations without adjusting entry slit widthof the photomultiplier. In additional embodiments, the method comprisescalculating sample concentration from the determined mean input current.

In another aspect, a method of detecting optical emission comprisingsimultaneously detecting a current signal, e.g., input current signal oroutput current signal, of at least two internal dynodes of aphotomultiplier configured to receive photons, and averaging thedetected current signals at each of the at least two internal dynodescomprising a measured current signal above a noise current signal andbelow a saturation current signal to determine a mean input current isdisclosed.

In certain examples, the method comprises terminating signalamplification at a dynode where a saturation current is measured. Inother examples, the method comprises simultaneously detecting a currentsignal at every other internal dynode of the plurality of dynodes. Infurther embodiments, the method comprises simultaneously detecting acurrent signal at every third internal dynode of the plurality ofdynodes. In some examples, the method comprises terminating signalamplification at a dynode where a saturation current is measured. Inadditional examples, the method comprises providing a floating voltageat each detected dynode of the plurality of dynodes. In other examples,the method comprises controlling the voltage at each dynodeindependently of voltage at the other dynodes of the plurality ofdynodes. In some embodiments, the method comprises measuring opticalemission from a plurality of samples comprising different concentrationswithout adjusting the gain of the photomultiplier. In further examples,the method comprises measuring optical emission from a plurality ofsamples comprising different concentrations without adjusting entry slitwidth of the photomultiplier. In some embodiments, the method comprisescalculating sample concentration from the determined mean current. Insome examples, the method comprises determining the mean current bycalculating the currents at selected dynodes and discarding calculatedcurrents below the noise current signal and above the saturation currentsignal, and scaling each non-discarded calculated current by itsrespective gain and averaging the scaled currents to determine the meancurrent.

In another aspect, a method of measuring photons comprising separatelycontrolling a bias voltage in each dynode of an optical detectorcomprising a photocathode, an anode and a plurality of dynodes betweenthe photocathode and the anode to measure the photons is provided.

In certain embodiments, the method comprises regulating the dynodevoltage to be substantially constant. In certain examples, the methodcomprises calculating currents, e.g., input current or output currents,at selected dynodes of the plurality of dynodes, discarding calculatedcurrents below a noise current level and above the saturation currentlevel, scaling each non-discarded calculated current by its respectivegain, and averaging the scaled currents to determine a mean current.

In an additional aspect, a method of analyzing a sample comprisingamplifying a light signal from the sample by independently measuring acurrent, e.g., input current or output current, at each of a pluralityof dynodes in an optical detector comprising a photocathode, an anodeand the plurality of dynodes between the photocathode and the anode isprovided. In certain embodiments, the method comprises calculatingcurrents at each dynode of the plurality of dynodes, discardingcalculated currents below a noise current level and above the saturationcurrent level, scaling each non-discarded calculated current by itsrespective gain, and averaging the scaled currents to determine a meancurrent.

In another aspect, a method of analyzing a sample comprising amplifyinga light signal from the sample by independently measuring a current,e.g., input current or output current at two or more of a plurality ofdynodes in an optical detector comprising a photocathode, an anode andthe plurality of dynodes between the photocathode and the anode isdescribed. In certain examples, the method comprises calculatingcurrents at each of the two or more dynodes of the plurality of dynodes,discarding calculated currents below a noise current level and above asaturation current level, scaling each non-discarded calculated currentby its respective gain, and averaging the scaled currents to determine amean current. In other examples, the method comprises measuring currentsfrom every other dynode of the plurality of dynodes.

In an additional aspect, a system comprising a photocathode, an anode, aplurality of dynodes between the photocathode and the anode, at leastone electrometer electrically coupled to one of the plurality ofdynodes, and a processor electrically coupled to the at least oneelectrometer, the processor configured to determine a mean current,e.g., input current or output current, from currents measured by theelectrometer. In certain examples, the processor is configured todetermine the mean current by calculating currents at the at least onedynode of the plurality of dynodes, discarding calculated currents belowa noise current level and above the saturation current level, scalingeach non-discarded calculated current by its respective gain, andaveraging the scaled currents to determine a mean current. In someexamples, the system comprises a second electrometer electricallycoupled to a dynode other than the dynode electrically coupled to theelectrometer. In additional examples, the processor is configured todetermine the mean current by calculating currents at the dynodeelectrically coupled to the electrometer and at the dynode electricallycoupled to the second electrometer, discarding calculated currents belowa noise current level and above the saturation current level, scalingeach non-discarded calculated current by its respective gain, andaveraging the scaled currents to determine a mean current. In someembodiments, each of the plurality of dynodes is electrically coupled toa respective electrometer. In other embodiments, the processor isconfigured to determine the mean current by calculating currents at eachdynode of the plurality of dynodes, discarding calculated currents belowa noise current level and above the saturation current level, scalingeach non-discarded calculated current by its respective gain, andaveraging the scaled currents to determine a mean input current.

Additional attributes, features, aspects, embodiments and configurationsare described in more detail herein.

BRIEF DESCRIPTION OF THE FIGURES

Certain features, aspects and embodiments of the signal multipliers aredescribed with reference to the accompanying figures, in which:

FIG. 1 is an illustration of a detector comprising a photocathode, ananode and a plurality of dynodes between them, in accordance withcertain examples;

FIG. 2 is an illustration of a detector where each dynode iselectrically coupled to an electrometer, in accordance with certainexamples;

FIG. 3 is an illustration of detector where every other dynode iselectrically coupled to an electrometer, in accordance with certainexamples;

FIG. 4 is an illustration of a detector where every third dynode iselectrically coupled to an electrometer, in accordance with certainexamples;

FIG. 5 is an illustration of a detector where every fourth dynode iselectrically coupled to an electrometer, in accordance with certainexamples;

FIG. 6 is an illustration of a detector where every fourth dynode iselectrically coupled to an electrometer, in accordance with certainexamples;

FIG. 7 is a chart showing a signal intensity range for each of aplurality of dynodes, in accordance with certain examples;

FIG. 8 is an illustration showing the use of a resistor ladder tocontrol the voltage of dynodes in a detector, in accordance with certainexamples;

FIG. 9 is an illustration showing the use of a plurality ofelectrometers each electrically coupled to a respective dynode, inaccordance with certain examples;

FIG. 10 is an illustration showing a power converter electricallycoupled to an amplifier to provide power to the amplifier, in accordancewith certain examples;

FIG. 11 is an illustration showing an circuit configured to provideseparate control of the dynode bias voltages in a detector, inaccordance with certain examples;

FIG. 12 is a schematic of a circuit configured to terminateamplification of a signal in response to saturation of a dynode, inaccordance with certain examples;

FIG. 13 is a chart illustration showing the dynamic range of variousdynodes, in accordance with certain examples;

FIG. 14A is a circuit configured to control dynode voltage, inaccordance with certain examples;

FIGS. 14B and 14C together show a schematic of another circuitconfigured to control dynode voltage, in accordance with certainconfigurations;

FIG. 15 is an illustration of a side-on detector in accordance withcertain examples;

FIG. 16 is an example of a device for optical emission spectroscopy, inaccordance with certain examples;

FIG. 17 is an example of a device for measuring fluorescence orphosphorescence, in accordance with certain examples;

FIG. 18 is a schematic of a confocal microscope, in accordance withcertain examples;

FIG. 19 is a schematic of a scintillation camera, in accordance withcertain examples;

FIG. 20A is an illustration of a microchannel plate, in accordance withcertain examples;

FIG. 20B is an illustration of stacked microchannel plates each of whichcan function as a dynode, in accordance with certain configurations;

FIG. 21 is schematic of an image intensifier, in accordance with certainexamples; and

FIG. 22 is a simplified illustration of a continuous optical detector,in accordance with certain configurations.

It will be recognized by the person of ordinary skill in the art, giventhe benefit of this disclosure, that the components in the figures arenot limiting and that additional components may also be included withoutdeparting from the spirit and scope of the technology described herein.

DETAILED DESCRIPTION

Certain features, aspects and embodiments described herein are directedto optical detectors and systems using them that can receive incidentphotons, amplify a signal corresponding to the photons and provide aresulting current or voltage. In some embodiments, the optical detectorsand systems described herein can have an extended dynamic range,accepting large electron currents and high levels of light, withoutdamaging or prematurely aging the device. In other instances, theoptical detectors and systems may be substantially insensitive tooverloading or saturation effects as a result of high concentrations (orhigh amounts of photons emitted or otherwise provided to the opticaldetector) while still providing rapid acquisition times and accuratemeasurements.

In some embodiments, the dynodes of the optical detectors describedherein can be used to measure signals, e.g., signals representative ofthe incident light, in a manner that does not overload the dynodes. Forexample, the detectors can be configured such that dynodes downstream ofa saturated dynode are “shorted out” or not used in the amplification.This configuration can increase the lifetime of the optical detectorsand can permit use of the optical detectors over a wide concentrationrange of sample without having to alter or adjust the gain of theoptical detectors for each concentration. For example, the voltage (orcurrent) of each dynode can be monitored and/or used to measure thesignal. If desired, dynodes that provide a signal above a noise leveland/or below a saturation level can be monitored and grouped together,e.g., to provide a mean signal that can be used to determineconcentration or otherwise provide a desired output, e.g., an image,that corresponds to the incident light. Where dynode saturation ismeasured, signal amplification can be terminated at dynodes downstreamof the saturated dynode, or optionally at the saturated dynode itself,to enhance the lifetime of the optical detectors and systems. Referenceto the terms “upstream” and “downstream” is understood to refer to theposition of one dynode relative to another dynode. For example, a dynodeof a photomultiplier that is immediately adjacent to a photocathodewould be upstream of a dynode that is immediately adjacent to an anodeof the photomultiplier. Similarly, a dynode of a photomultiplier that isimmediately adjacent to the anode would be downstream of a dynode thatis immediately adjacent to the photocathode of the photomultiplier.

In certain embodiments, the optical detectors and systems describedherein have wide applicability to many different types of opticaldevices including, but not limited to, optical detectors of medical andchemical instrumentation, microscopes, cameras, telescopes, microchannelplate detectors, CT scanners, PET scanners, X-ray detectors, imageintensifiers, vision devices, e.g., night vision devices, radiationdetectors and other optical devices that amplify light signals toprovide a current (or voltage), image or signal representative ofincident light. The optical devices may be used with, or may include,one or more scintillators, primary emitters, secondary emitters or othermaterials to facilitate light detection and/or use of the light toprovide an image. Visual imaging components can be used with themeasured signals to construct images representative of the lightreceived by the detectors and systems described herein. Examples ofthese and other optical detectors and systems are described in moredetail below.

Certain figures are described below in reference to devices includingdynodes or dynodes stages. It will be recognized by the person ofordinary skill in the art, given the benefit of this disclosure, thatthe exact number of dynodes or dynode stages can vary, e.g., from 5 to30 or any number in between or other numbers of dynode stages greaterthan 30, depending on the desired signal amplification, the desiredsensitivity of the device and other considerations. In addition, wherereference is made to channels, e.g., channels of a microchannel platedevice, the exact number of channels may also vary as desired. In someconfigurations, the dynodes may be present in a continuous dynodedevice.

In certain embodiments and referring to FIG. 1, certain components of anoptical detector 100 are shown. The detector 100 comprises aphotocathode 115, an anode 135, and a plurality of dynodes 125-133between the photocathode 115 and the anode 135. While not shown, thecomponents of the detector 100 would typically be positioned within atube or housing (under vacuum) and may also include a focusing electrodebetween the photocathode 115 and the first dynode 126 of the pluralityof dynodes 125 to orient the beam from the photocathode 115 at asuitable angle. In use of the detector 100, light beam 110 is incidenton the photocathode 115, which converts the optical signal from thelight beam 110 into an electrical signal shown as beam 120 by way of thephotoelectric effect. In some embodiments, the photocathode 115 can bepresent as a thin film or layer on an entry aperture of the detector100. The energy from the light beam 110 is converted by the photocathode115 into an electrical signal by emission of electrons from thephotocathode 115. For example, an incident photon can strike the surfaceof the photocathode 115 and cause ejection of electrons from the surfaceof the photocathode 115. The exact number of electrons ejected perphoton depends, at least in part, on the work function of the materialand the energy of the incident photon. The beam 120 is incident on adownstream dynode 126, which emits secondary electrons in the generaldirection of the dynode 127. For example, a voltage-divider circuit (asdescribed below), or other suitable circuitry, can be used to provide amore positive voltage for each downstream dynode. The potentialdifference between the photocathode 115 and the dynode 126 causeselectrons ejected from the photocathode to be accelerated toward thedynode 126. The exact level of acceleration depends, at least in part,on the gain used. Dynode 127 is typically held at a more positivevoltage than dynode 126, e.g., 100 to 200 Volts more positive, to causeacceleration of electrons emitted by dynode 126 toward dynode 127. Aselectrons are emitted from the dynode 127, they are accelerated towarddownstream dynode 128 as shown by beams 140. A cascade mechanism isprovided where each successive dynode stage emits more electrons thanthe number of electrons emitted by an upstream dynode. The resultingamplified signal is provided to the anode 135, which typically outputsthe current to an external circuit through one or more electricalcouplers of the optical detector 100. The current measured at the anode135 can be used to determine the amount of light emitted by a sample. Ifdesired, the measured current can be used to quantitate theconcentration or amount of sample using conventional standard curvetechniques. In general, the detected current depends on the number ofelectrons ejected from the photocathode 115, which is proportional tothe number of incident photons and the gain of the device 100. Gain istypically defined as the number of electrons collected at the anode 135relative to the number of electrons ejected from the photocathode 115.For example, if 5 electrons are emitted at each dynode, and the device100 includes 8 total dynodes, then the gain is 5⁸ or about 390,000. Thegain is dependent on the voltage applied to the device 100. For example,if the voltage is increased, the potential differences between dynodesare increased, which results in an increase in incident energy ofelectrons striking a particular dynode stage.

In some embodiments, the optical detector 100 can be overloaded bypermitting too much light to be introduced into the housing and/or byadjusting the gain to be too high. As noted above, the gain of existingoptical detectors can be adjusted by changing or adjusting a controlvoltage to provide a desired signal without saturation of the detector.For example, the operating voltage of a typical detector may be between800-3000 Volts. Changing the operating voltage can result in a change inthe gain. Typical gain values may be from about 10⁵ to about 10⁸. Thegain adjustment often takes place from sample to sample to avoidoverloading the detector at high sample concentrations (or high amountsof light) and to avoid not providing enough signal amplification at lowconcentrations of sample (or low levels of incident light).Alternatively, a gain can be selected (by selecting a suitable operatingvoltage) so that the more intense samples do not saturate the detector.Adjusting the gain from measurement-to-measurement or image-to-imageincreases sampling time, can reduce detector response time and may leadto inaccurate results. Where the gain is too high, the detector canbecome overloaded or saturated, which can result in reduced lifetime forthe detector and provide inaccurate measurements. Where the gain is toolow, low levels of light may go undetected. In certain embodimentsdescribed herein, the gain of the detector can be kept constant and canbe rendered insensitive to saturation or overloading at high levels oramounts of light entering into the detector. Instead, the current atselected dynode stages can be monitored and used to determine whether ornot signal amplification using downstream dynodes should continue or ifamplification should be terminated to protect the detector, e.g., toprotect the dynode surfaces. The measured current at selected dynodestages can be scaled by their stage gain and then averaged or otherwiseused to determine a mean input current signal that is representative ofthe concentration or amount of light that arrives at the detector.Illustrations of such processes are described in more detail below.

In certain embodiments, each of the dynodes 126-133 (and collectivelyshown as element 125) of the optical detector 100 can be configured toelectrically couple to an electrometer so that the input current (oroutput current) at each of the plurality of dynodes 125 can be monitoredor measured. In some configurations, the voltage difference between eachdynode may be around 100 to 200V. As described elsewhere herein, theelectrometer may part of an analog circuit or a digital circuit. Forexample, a solid-state amplifier comprising one or more field-effecttransistors can be used to measure the current at each of the pluralityof dynodes 126-133. In some instances, each of the plurality of dynodes126-133 may include a respective solid-state amplifier. If desired, theamplifier can be coupled to one or more signal converters, processors orother electrical components. In combination, the components may provideor be considered a microcontroller comprising one or more channels,e.g., ADC channels. In some embodiments, a single microprocessor can beelectrically coupled to one, two or more, e.g., all, of the dynodes suchthat current values can simultaneously be provided to the processor forthe one, two or more, e.g., all, dynodes. Because of the differentdynode voltages, the current values can be provided by way of some meansof electrically isolating the various signals from each dynode, e.g.,optocouplers, inductors, light pipe, IRF devices or other components canbe used. For example, each dynode/electrometer pair can be electricallyisolated and/or electrically insulated from other dynode/electrometerpairs such that separate signals can be measured from each of thedynodes. In other configurations, a processor electrically coupled tosuitable components (as described herein) can monitor current levels ateach dynode and can be used to determine a mean input current fordetermining a concentration of a sample or for constructing an imagebased on the determined inputs.

In certain embodiments and referring to FIG. 2, one configuration ofcertain components in an optical detector system are shown. In FIG. 2,an optical detector 200 comprises a photocathode 210, an anode 220, anda plurality of dynodes stages 230-237. In the detector 200, each of thedynode stages 230-237 is electrically coupled to a respectiveelectrometer 240-247. The electrometers 240-247 can each be electricallycoupled to a first processor 250, e.g., through separate input channels(not shown) of the processor 250. If desired, the anode 220 can also beelectrically coupled to an optional electrometer 252. For example, incertain instances it may be desirable to switch operation of thedetector 200 from the state where one or more internal dynode currentsare monitored to a second state where only current at the anode 220 ismonitored. As noted herein, the processor 250 may be present on aprinted circuit board, which may include other components commonly foundon printed circuit boards including, but not limited to, I/O circuits,data buses, memory units, e.g., RAM, clock generators, supportintegrated circuits and other electrical components. While not shown,the dynodes/electrometer pairs of the detector 200 may be electricallyisolated from each other to provide separate signals to the firstprocessor 250.

In other embodiments and referring now to FIG. 3, it may not bedesirable to monitor the current at each dynode of the detector. Forexample, in an optical detector 300, every other dynode is electricallycoupled to an electrometer. The detector 300 comprises a photocathode310, an anode 320, and a plurality of dynodes stages 330-337 are shown.In the detector 300, every other dynode stage is electrically coupled toa respective electrometer. For example, dynode stages 330-333 are notelectrically coupled to an electrometer, and each of dynode stages334-337 is electrically coupled to a respective electrometer 344-347.The electrometers 344-347 can each be electrically coupled to a firstprocessor 350, e.g., through separate input channels (not shown) of theprocessor 350. If desired, the anode 320 can also be electricallycoupled to an optional electrometer 352. As noted herein, the processor350 can be present on a printed circuit board, which may include othercomponents commonly found on printed circuit boards including, but notlimited to, I/O circuits, data buses, memory units, e.g., RAM, clockgenerators, support integrated circuits and other electrical components.By configuring the detector with an electrometer on every otherelectrode, detector fabrication and reduced circuitry can beimplemented. As noted in more detail below, selected current inputs fromthe detector 300 can be used to determine a mean input current, whichcan be used for calculating a sample concentration, reconstructing animage or for other means. While the configuration shown in FIG. 3illustrates an electrometer being present at every other dynode, it maybe desirable to include an electrometer on adjacent dynodes followed bya dynode stage without an electrometer rather than spacing theelectrometers on an every other dynode basis. For example, where adetector comprises eight dynodes and four electrometers, it may bedesirable to omit electrometers from all stages except the final fourdynode stages 332, 333, 336 and 337. While not shown, thedynodes/electrometer pairs of the detector 300 may be electricallyisolated from each other to provide separate signals to the firstprocessor 350.

In additional embodiments and referring to FIG. 4, it may be desirableto configure the detector with an electrometer on every third dynode.For example, a detector 400 comprises a photocathode 410, an anode 420and a plurality of dynodes 430-437 between the photocathode 410 and theanode 420. In the detector 400, every third dynode stage is electricallycoupled to a respective electrometer. For example, each of dynode stages434, 432 and 437 is coupled to an electrometer, 444, 442 and 447,respectively, and all other dynode stages are not coupled to anelectrometer. The electrometers 444, 442 and 447 can each beelectrically coupled to a first processor 450, e.g., through separateinput channels (not shown) of the processor 450. If desired, the anode420 can also be electrically coupled to an optional electrometer 452.While three electrometers are shown as being present in the detector400, the three electrometers could, if desired, be positioned togetherin the middle of the dynode stages, together toward one end of thedynode stages or spaced in some other manner than every third dynode.For example, it may be desirable to omit electrometers from all stagesexcept the final three dynode stages 433, 436 and 437. Additionalconfigurations of a detector comprising three electrometers eachelectrically coupled to a respective dynode will be readily selected bythe person of ordinary skill in the art, given the benefit of thisdisclosure. While not shown, the dynodes/electrometer pairs of thedetector 400 may be electrically isolated from each other to provideseparate signals to the first processor 450.

In other embodiments and referring to FIG. 5, it may be desirable toconfigure the detector with an electrometer on every fourth dynode. Forexample, a detector 500 comprises a photocathode 510, an anode 520 and aplurality of dynodes 530-537 between the photocathode 510 and the anode520. In the detector 500, every fourth dynode stage is electricallycoupled to a respective electrometer. For example, each of dynode stages535 and 537 is coupled to an electrometer, 545 and 547, respectively,and all other dynode stages are not coupled to an electrometer. Theelectrometers 545 and 552 can each be electrically coupled to a firstprocessor 550, e.g., through separate input channels (not shown) of theprocessor 550. If desired, the anode 520 can also be electricallycoupled to an optional electrometer 552. While two electrometers areshown as being present in the detector 500, the two electrometers could,if desired, be positioned together in the middle of the dynode stages,together toward one end of the dynode stages or spaced in some othermanner than every fourth dynode. For example, it may be desirable toomit electrometers from all stages except the final two dynode stages533 and 537. Additional configurations of a detector comprising twoelectrometers each electrically coupled to a respective dynode will bereadily selected by the person of ordinary skill in the art, given thebenefit of this disclosure. While not shown, the dynodes/electrometerpairs of the detector 500 may be electrically isolated from each otherto provide separate signals to the first processor 550.

In some examples, it may be desirable to configure the detector with anelectrometer on every fifth dynode. For example and referring to FIG. 6,a detector 600 comprises a photocathode 610, an anode 620 and aplurality of dynodes 630-637 between the photocathode 610 and the anode620. In the detector 600, every fifth dynode stage is electricallycoupled to a respective electrometer. For example, each of dynode stages633 and 634 is coupled to an electrometer 643 and 644, respectively, andall other dynode stages are not coupled to an electrometer. Theelectrometers 643 and 644 can each be electrically coupled to a firstprocessor 650, e.g., through separate input channels (not shown) of theprocessor 650. If desired, the anode 620 can also be electricallycoupled to an optional electrometer 652. While two electrometers areshown as being present in the detector 600, the two electrometers could,if desired, be positioned together in the middle of the dynode stages,together toward one end of the dynode stages or spaced in some othermanner than every fifth dynode. In addition, the electrometer couplingneed not occur on the second and seventh dynode stages 634 and 633,respectively, but instead may be present on the first dynode 630 andsixth dynode 636, the third dynode 631 and the eighth dynode 637 orother dynodes spaced apart by four dynode stages. While not shown, thedynodes/electrometer pairs of the detector 600 may be electricallyisolated from each other to provide separate signals to the firstprocessor 650.

While FIGS. 2-6 show particular electrometer spacing, where more thaneight dynode stages are present, the spacing may be different than theparticular spacing shown in FIGS. 2-6. For example, the spacing may begreater than every fifth dynode where more than eight dynodes arepresent, may be concentrated toward the middle dynode stages, may beconcentrated toward dynode stages near the anode or may otherwise bespaced in a desired or selected manner. In some instances where atwenty-six dynode electron multiplier is used, a first electrometer maybe present at a mid-point, e.g., electrically coupled to dynode 13, anda second electrometer can be positioned upstream of dynode 13 ordownstream of dynode 13.

In certain embodiments, in operation of the detectors and systemsdescribed herein, the signal, e.g., input current or output current, canbe monitored at the various dynode stages, e.g., this current will be aninput current if the next dynode is positively biased or an outputcurrent otherwise. This signal can be used to determine a mean currentsignal, which may be used for qualitative purposes, quantitativepurposes or used in image construction. Referring to the schematic shownin FIG. 7, illustrative signal values for a detector comprising twelvedynode stages is shown. The bars for each dynode represent the dynamicrange of each of the dynodes. For exemplary purposes, dynode 1 isconsidered to be the dynode immediately adjacent to and downstream ofthe photocathode (or where the detector does not include a photocathode,dynode 1 is the dynode closest to an opening aperture that receives theincident light from a sample or light reflected or emitted from anobject). A lower signal limit 710 can be selected by the processor suchthat an output signal below the lower limit is considered to be withinthe noise, e.g., has a signal-to-noise ratio of less than 3. Thesesignals can be discarded. Similarly, an upper signal limit 720 can beselected where values above the upper limit are considered to besaturated dynodes. These values can also be discarded by the processor.Additionally, as described below, where a saturated dynode is detected,dynodes downstream of the saturated dynode can be shorted out, makingthe saturated dynode function as a collector plate to pull out allelectrons to protect the detector. No signals are shown in FIG. 7 fordynodes 11 and 12 as those dynodes are downstream of the saturateddynode (dynode 10). The remaining values within the selected currentwindow (signals for dynodes 3-9) can be used to determine a mean signal.For example, if the output current is monitored and the gain of thedynode stages is known, then a mean signal can be determined for thevarious dynode stages using the current and the gain values.Alternatively, the input current at each dynode can be measured andconverted simultaneously. For example, the input current can be computedat each dynode using the gain curve of the dynodes. The input currents(for all input current below saturated dynodes and input currents abovedynodes above the signal-to-noise) can simultaneously be averaged, e.g.,after normalizing each using the gain, to determine a mean input currentthat corresponds to the light signal incident on the optical detector.Additionally, the detector can be configured to shut down dynodes wheresaturation is observed. For example, if saturation is observed at anydynode stage, then that dynode stage or subsequent downstream dynodestages can be shut down, e.g., by altering the voltage at downstreamdynodes to stop the cascade, to protect the remaining dynodes of thedetector, which can extend detector lifetimes. The averaging of signalsand monitoring of individual dynodes can be performed in real time toextend the dynamic range of the detectors, e.g., the dynamic range canbe extended by the gain.

In certain embodiments and referring to FIG. 8, a conventional schematicof certain components of a detector are shown. Five dynodes 810-815 ofthe detector 800 are shown, though as indicated by the curved linesbetween dynodes 812 and 813 additional dynode stages can be present. Thedetector 800 also includes a photocathode (not shown) upstream of thedynode 810. A resistor ladder 830 is used to electrically biasdownstream dynodes to have a more positive voltage than upstreamdynodes, which results in acceleration of electrons and amplification ofthe signal 805. For example, the voltage of the first dynode 810 isselected such that electrons striking the dynode 810 will be ejected andaccelerated toward the second dynode 811. The bias voltage of thevarious dynodes 810-814 is achieved by selecting suitable resistorvalues in the resistor ladder 830. For example, the resistor values areselected to supply the difference between the input current minus theoutput current for each dynode, while substantially maintaining the biasvoltage. As shown in FIG. 8, an amplifier 840, e.g., an amplifier withfeedback, that is electrically coupled to an analog-to-digital converter850 can be present to send digital signals to a processor (not shown)for measuring the current at the dynode 815.

In certain configurations of the detectors described herein, thesupplied current to each dynode can be a direct measure of the electroncurrent. An electrometer can be used to measure the input current ateach dynode without disturbing or altering the other dynode stages.Generally, an amplifier can be coupled to each dynode bias voltage tocreate a virtual ground at the bias voltage. The output voltage withrespect to the virtual ground is proportional to the dynode currentmultiplied by the resistance of the feedback resistor. Each signal fromthe amplifier can then be converted, e.g., using an analog-to-digitalconverter, and the resulting values can be provided to a processorthrough some means of electrical insulation (or electrical isolation orboth) for use in determining a mean input or output current from thosesignals below a saturation level and above a noise level. Oneillustration of such a configuration is shown in FIG. 9 where threedynode stages are shown for representative purposes. A dynode 911 isshown as being electrically coupled to an amplifier 921 and a signalconverter 931. A resistor 941 is electrically coupled to the amplifier921. The amplifier 921 is coupled to the dynode bias voltage of dynode911 to create a virtual ground at the bias voltage. The dynode biasvoltage can be provided using resistor ladder 905 as described, forexample, in reference to the resistor ladder of FIG. 8. The outputvoltage with respect to the virtual ground is proportional to thecurrent from the dynode 911 multiplied by the resistance of the feedbackresistor 941. The output from the amplifier 921 can then be converted bysignal converter 931, and the resulting value can be provided to aprocessor 950 for use in determining a mean input current if the signalfrom the dynode 911 is within an acceptable signal window, e.g., iswithin a window or range between a saturation level signal and a noiselevel signal. The input current (or output current) at dynode 912 mayalso be measured in a similar way. In particular, an amplifier 922 iselectrically coupled to the dynode 912 and to a signal converter 932. Aresistor 942 is electrically coupled to the amplifier 922. The amplifier922 is coupled to the dynode bias voltage of dynode 912 to create avirtual ground at the bias voltage. The output voltage with respect tothe virtual ground is proportional to the current from the dynode 912multiplied by the resistance of the feedback resistor 942. The outputfrom the amplifier 922 can then be converted by signal converter 932,and the resulting value can be provided to the processor 950 for use indetermining a mean input current if the signal from the dynode 912 iswithin an acceptable signal window, e.g., is within a window or rangebetween a saturation level signal and a noise level signal. The currentmay be measured at dynode 913 in a similar way using the amplifier 923,the signal converter 933, the feedback resistor 943 and the processor950. If desired, digital signals can be provided such that measuredcurrents within an acceptable window comprise words or signals that areused by a processor to determine a mean input current, and signals thatare not acceptable, e.g., within the noise or representative ofsaturated signals, are coded differently, e.g., have different words orsignals, and are not used by the processor in the calculation.

In certain examples, while all three dynodes in FIG. 9 are shown asincluding a respective electrometer, it may be desirable to include onlytwo electrometers, e.g., the current at dynode 912 may not be monitored.In some embodiments described herein, the detectors and system caninclude two, three, four, five or more electrometers coupled to internaldynodes, e.g., those between a first dynode and an anode, to providesufficient signals in determining mean input signals. If desired, eachinternal dynode can include a respective electrometer to increase theoverall accuracy of the measurements. In certain embodiments where theelectrometer floats at the dynode bias voltage, the power for eachelectrometer and any associated signal converters can be provided from afloating DC/DC converter. Referring to FIG. 10, a single dynode 1010 isshown as being electrically coupled to an amplifier 1020. The amplifier1020 floats at the bias voltage of the dynode 1010. A floating DC/DCconverter 1030 can be electrically coupled to the amplifier 1020 and asignal converter 1040 to provide power to these components. The DC/DCconverter 1030 typically converts a higher voltage, e.g., 24 Volts, to alower voltage, e.g., 5 Volts, that is provided to the amplifier 1020 andthe signal converter 1040. Power converters other than DC/DC convertersmay also be used in the configuration shown in FIG. 10 to provide powerto the electrometer. If desired, each dynode can be electrically coupledto a power converter. In some embodiments, only those dynodeselectrically coupled to an electrometer are also electrically coupled toa power converter. If desired, the first dynode 1010 can be held at afixed offset, which can assist in keeping the electron conversionsconstant.

In certain examples, the dynode bias voltage, as described herein, canbe provided by selecting suitable resistors in the resistor ladder. Thisconfiguration changes the dynode to dynode voltage and can introduceerrors. For example, at 3 kV, an error up to 3 Watts can be introduced.To avoid this error, it may be desirable to regulate each dynode voltageto reduce any errors that may be introduced from voltage changes withincreased electron currents. One configuration that permits controllingthe dynode voltages separately is shown in FIG. 11. To achieve asubstantially constant voltage, a Zener diode or a regulated amplifiercan be used. The device includes dynodes 1110 and 1111 electricallycoupled to amplifiers 1120 and 1121, respectively, similar to theconfiguration described in reference to FIG. 10. An amplifier 1131 canbe electrically coupled to the resistor ladder 1105 and to a Zener diode1141 to provide for independent control of the voltage provided to thedynode 1110. For example, the Zener diode 1141 is electrically coupledto an input of the amplifier 1131 to provide for additional control ofthe bias voltage for the dynode 1110, e.g., to limit or clip the voltageif desired or needed and generally aid in providing a bias voltage tothe dynode 1110 that does not vary substantially as electron currentsincrease at other dynodes of the detector. Similarly, a Zener diode 1142is electrically coupled to an input of an amplifier 1132 to permitcontrol of the bias voltage to dynode 1111. An electrometer can beelectrically coupled to each of the dynodes 1110 and 1111. For example,an amplifier 1120 can be electrically coupled to the dynode 1110 andused to provide a signal to a signal converter 1150, which may convertthe signal, e.g., to a digital signal, and provide the converted signalto a processor (not shown). Similarly, an amplifier 1121 can beelectrically coupled to the dynode 1111 and used to provide a signal toa signal converter 1151, which may convert the signal, e.g., to adigital signal, and provide the converted signal to a processor (notshown). Where the detector includes more than two dynodes, there can bemultiple voltage controllers, e.g., similar to the amplifier/Zener diodecombination shown in FIG. 11, between dynodes to separately control thedynode to dynode voltage of the detector. If desired, there need not bevoltage control between each dynode node. For example, it may bedesirable to omit voltage control between certain dynodes to simplifythe overall construction of the detector. In the configuration shown inFIG. 11, the resistor chain can use very low current, e.g., less than0.1 mA, which reduces generated heat and current demand on the detectorpower supply, which is typically a 3 kV power supply.

In certain embodiments, at high levels of incident light, the downstreamdynodes, e.g., those closer to the anode, may begin to saturate. Forexample, as the input current increases, the downstream dynode stageswill start to saturate the amplifiers and the signal converters. Whilethe electronics are not likely to be damaged from saturation, thematerials present on the dynode that eject electrons can be damaged.Damage or deterioration of the dynode surface can result in a change inthe local gain of a particular dynode, which can lead to measurementerrors. Desirably, the dynode voltages are selected to overlap well withthe dynamic range of each detector. It is desirable, for example, tooverlap more than 50% to achieve a linear output. Where such a gain isselected for a certain light intensity and a subsequent measurement isperformed with incident light of higher intensity, it may be desirableto stop the amplification of the signal at a dynode where saturation isdetected. In some embodiments, the saturated dynode may be the lastdynode where the signal is amplified, e.g., the saturated dynode mayfunction as an anode, whereas in other examples, a dynode downstream ofthe saturated dynode can be shorted out to act like an anode to removeall electrons. Many different mechanisms can be used to terminate signalamplification. In one embodiment, the bias voltage of a dynode adjacentto and downstream of a saturated dynode can be adjusted such thatelectrons are not accelerated from the saturated dynode toward theadjacent dynode. In this manner, the signal amplification will beinterrupted at the saturated dynode.

Referring to FIG. 12, a schematic is shown of a circuit that can beimplemented to terminate signal amplification in the detectors andsystems described herein. The components not labeled in FIG. 12 aresimilar to those described and shown in reference to FIG. 11. At thesaturation level, a downstream dynode 1211 (downstream relative to asaturated dynode 1210) can be biased slightly positive in respect to thesaturated dynode 1210. For example, the node can shorten the voltagedivider on the dynode stage below, to +5V node of the saturation dynode.If a reference voltage of about 2 Volts is present, the dynode 1211below will end up about +3V over the saturated dynode. The output signalof the saturated dynode will become an anode and will collect allelectron currents. The ADC will saturate in the reverse polarity. Ifdesired, this configuration can be used to clamp the dynode gain voltagedirectly, or can be detected by the control system. For example, as theincident signal changes, the particular dynode where signal terminationoccurs may change from measurement to measurement. Desirably, theprotection switching speed can be close to the ADC conversion speed, sosignal termination can be implemented before any damage to downstreamdynodes can occur.

It is a substantial attribute of embodiments described herein that bystopping the signal amplification at a saturated dynode (or a dynodedownstream from a saturated dynode), the gain of the device can be fixedand not user adjustable. For example, in a detector operated at a fixedgain and with 26 dynodes, if saturation is detected at dynode 23, thenamplification may be terminated by shorting out the amplification at thedynode 23. For a subsequent measurement or receipt of photons at thesame fixed gain, the number of photons (or photon intensity) may be suchthat saturation occurs at dynode 19. Amplification can be terminated atdynode 19 without having to adjust the gain, as would be required whenusing a typical photomultiplier tube. In this manner, a single fixedgain can be selected, and the detector can monitor the input currents ofthe dynodes to determine when signal amplification should terminate. Oneresult of such configurations is extending the dynamic range of thedetector without loss of linearity or detection speed. For example, ifthe current at each dynode is measured, then the dynamic range isextended by the gain. If a 16-bit analog-to-digital converter is used,then this is 65 k (2¹⁶) times the gain. Where the system is designed toterminate amplification at a saturated dynode, the detector can beoperated at a maximum voltage, e.g., 3 kV, to provide a maximum gain. Atthis voltage, a gain of 10⁷ would be anticipated in many detectors. Toaccount for noise and assuming a signal-to-noise of 10:1 for a singlephoton event, the dynamic range would be reduced by a factor of 10. Thetotal dynamic range when using a 16-bit ADC on every dynode would beexpected to be about 6×10¹⁰ (65,000 times 10⁶). If conversion of thereadings occurs at a frequency of 100 kHz, then about 100,000 differentsample measurements can be averaged to expand the dynamic range to atotal dynamic range of about 6×10¹⁵. For a particular sample, differentsamples varying greatly in intensities can be scanned and detectedwithout having to alter the gain of the detector.

In certain embodiments to demonstrate a typical output of dynodes, andaccounting for the dynamic range at each dynode, an illustration isshown in FIG. 13 of the dynode current for each dynode in a 13 dynodedetector relative to an input current. As shown in FIG. 13, the outputof the ADC's for Dynodes 1 and 2 is very low and within the electronicnoise. As such, these outputs are discarded and not considered in theinput calculations. Dynodes 3 to 10 provide ADC outputs within anacceptable window. The signal values of dynodes 3-10 can be averaged toprovide a seven-fold accuracy improvement over a single ADC reading.Dynode 11 is measured as being saturated, which results in switching offof dynodes 12 and 13 thus terminating the amplification at dynode 11.The measurement from dynodes 11-13 can also be discarded or otherwisenot used in averaging to provide a mean input current that correspondsto the light from a sample or image.

In certain examples and as described herein, measurement of a current atevery dynode is not required. Instead, every second, third or fourthdynode could be measured and used. The gain between each stage can beany value, and can be ‘calibrated’ by comparing its ADC reading to thestage below and above. This found gain can then be used as inputcurrent=sum of all stage gains time ADC reading. In some instances, thefixed voltage can be larger than the sum of all dynode stage voltages,and the bottom or last resistor can be used to absorb any extra voltage.In addition, the bottom resistor can also absorb any excess voltagegenerated by shorting a dynode for termination of signal amplification.In some configurations, it may be desirable to have enough dynodes tocompensate for eventual aging. For example, if EM gain decreases overtime due to deterioration of surface materials, the saturation point maymove further downstream in the dynode set. If the last dynode does notproduce an signal-to-noise of 10 to 1 (or other selectedsignal-to-noise) for single photon event, that response may beindicative that the detector has exceeded its useful life. The expecteddetector lifetime should be much larger than the current conventionalsystem due to signal termination at a saturated dynode and protection ofdownstream dynodes.

In certain embodiments, another schematic of a circuit that can be usedto measure the signal from a dynode is shown in FIG. 14A. The circuit1400 generally comprises an amplifier 1410 electrically coupled to acapacitor 1420 and a controller 1405 (or processor if desired). Thecircuit is electrically coupled to a dynode (not shown) throughcomponent 1430. Digital signals can be provided from a processor andused to control the bias voltage of the dynodes. For example, signalsfrom the processor can be used to short out the dynode, to regulate thedynode bias voltage or to otherwise assist in or control the signalamplification mechanism or terminate the signal amplification mechanism.

In certain configurations, another schematic of a circuit is shown inFIGS. 14B and 14C. The circuit has been split into two figures toprovide for a more user friendly version of the circuit. In theschematic NGND represent a virtual ground. The circuit comprises a DC/DCconverter U6 electrically coupled to amplifiers U16A and U16B to providea voltage to the dynode (labeled as node) of about 101 Volts. Areference voltage of about 4.096 volts is provided from a voltagereference U19 and can be used with the voltage from the DC/DC converterU6, e.g., using the outputs of amplifiers U16A and U16B and amplifierQ3, to provide the 101 Volts to the dynode. Analog signals from thedynode can be measured by an electrometer J4 and provided to ananalog-to-digital converter U12. The analog-to-digital converter U12 iselectrically coupled to digital isolators U23 and U24, which can isolatethe signals from the dynode. The outputted signals from each dynode canbe electrically insulated from the signals of other dynodes so that eachsignal from each dynode is separate from signals from other dynodes,which permits simultaneous measurement of signals from differentdynodes. To determine if a saturation signal is present at any onedynode, saturation threshold values can be set in software, and wheresaturation is detected at the dynode, the voltage can be clamped to stopamplification at the saturated dynode. For example, drive amplifier Q6and other components of the clamp can be used to short out the dynode,e.g., to place it at virtual ground NGND, which will stop signalamplification at that dynode. Each dynode of the dynode set may comprisea circuit similar to that shown in FIGS. 14B and 14C to provide forindependent voltage control, independent voltage clamping (if desired)and to provide separate, electrically isolated signals from eachnon-shorted dynode to a processor or other input device. In use of thecircuit of FIGS. 14B and 14C, dynode signals from dynodes of a dynodeset can be measured or monitored. Where a non-saturated signal isdetected, amplification may continue using downstream dynodes, e.g., byproviding a suitable voltage to the downstream dynodes. When asaturation signal is detected, the dynode where the saturation signal isobserved can be grounded to the virtual ground to terminate theamplification at that saturated dynode. Signals from dynodes downstreamof the clamped, saturated dynode generally represent noise signals as noamplification occurs at these downstream dynodes. Signals upstream ofthe saturated dynode and signals above a noise threshold value can beused, e.g., averaged, to determine a mean input current (or mean outputcurrent).

In certain embodiments, in implementing the detectors described herein,commercially available components can be selected and assembled as partof larger circuitry on a printed circuit board and/or as a separateboard or chip that can be electrically coupled to the dynodes. Certaincomponents can be included within the vacuum of the detectors, whereasother components may remain outside the vacuum tube of the detector. Forexample, the electrometers, over-current protections and voltagedividers can be placed into the vacuum tube as they do not produce anysubstantial heat that may increase dark current. To provide anelectrical coupling between the components in the vacuum tube and theprocessor of the system, suitable couplers and cabling, e.g., a flex PCBfeed cable that can plug into a suitable coupler, can be implemented.

In certain embodiments, the detectors described herein can be configuredas either side-on or end-on (also referred to as head-on) devices.Examples of end-on devices are pictorially shown in FIGS. 1-4, forexample, where the light is incident on an end of the detector. Thehousing of an end-on detector would typically be opaque such that theend of the detector near the photocathode is the only portion thatreceives any substantial light. In other configurations, a side-ondetector can be implemented in a similar manner as described herein,e.g., a side-on detector can include a plurality of dynodes with one,two, three or more (or all) of the dynodes electrically coupled to arespective electrometer. One illustration of a side-on detector is shownin FIG. 15. The detector 1500 comprises a photocathode 1510, which ispositioned on the side of the device. Light can enter an opticalaperture or window 1515 on the side of the detector 1500 and strike thephotocathode 1510. As described in reference to the end-on device, thephotocathode 1510 can emit electrons (shown as beam 1516) which areamplified by dynodes 1520-1526 within the device 1500 and collected bythe anode 1530. Selected dynodes of the side-on detector 1500 can beelectrically coupled to a respective electrometer and may includesuitable circuitry, e.g., similar to that described in connection withFIGS. 1-12, to permit measurement of input current at the dynodes1520-1526 and calculation of a mean input current signal, if desired.While an incident photon 1505 is shown in FIG. 15 as being incident atabout a ninety degree angle relative to the photocathode 1510, anglesother than ninety degrees can also be used. If desired, one or moreoptical elements, e.g., lenses, can be positioned between the window andthe incident light to provide light to the detector at a desired angle.

In certain examples, the exact dynode configuration present in anydetector can vary. For example, the dynode arrangement may be of themesh type, Venetian blind type, linear-focused type, box-and-grind type,circular-cage type, microchannel plate type, metal channel dynode type,electron bombardment type or other suitable configurations. In certainembodiments, the detectors described herein can be produced usingsuitable materials for the photocathode, the anode and the dynode. Forexample, the photocathode can include one or more of the followingelements or materials: Ag—O—Cs, GaAs:Cs, GaAs:P, InGaAs:Cs, Sb—Cs,Sb—K—Cs, Sb—Rb—Cs, Na—K—Sb—Cs, Cs—Te, Cs—I, InP/InGaAsP, InP/InGaAs, orcombinations thereof. The photocathodes can be configured astransmission (semitransparent) type or a reflection (opaque) type. Thedynodes of the detectors may include one or more of carbon (diamond),AgMg, CuBe, NiAl, Al₂O₃, BeO, MgO, SbKCs, Cs₃Sb, GaP:Cs or any one ormore of the materials described in connection with the photocathode. Asnoted herein, the exact material selected for use in the dynodes has adirect effect on the gain. One or more of these materials can be presenton a surface at a suitable angle to permit the surface to function as adynode. The anode may include suitable materials to permit collection ofany electrons, e.g., one or more conductive materials. The windows orapertures of the devices that are adjacent to the photocathode may beconfigured as optical filters, e.g., filters that permit only certainwavelengths to pass, or may be optically transparent. Typical glassmaterials used in the windows include, but are not limited to,borosilicate glass, low potassium glass, silica glass, UV glass, Schottglass, magnesium fluoride or other suitable glass materials. In otherembodiments, crystals or sapphire can be present between the housing ofthe detector (or in the housing of the detector) and the photocathodeand can function as optical apertures between the incident light and thephotocathode.

In certain examples, the detectors described herein can be used in manydifferent applications including, but not limited to, medical andchemical instrumentation, microscopes, cameras, telescopes, microchannelplate detectors, CT scanners, PET scanners, X-ray detectors, imageintensifiers, vision devices, e.g., night vision devices, radiationdetectors. Illustrations of these and other detectors are described inmore detail below.

In certain embodiments, the detectors and associated circuitry describedherein can be used in medical and chemical instrumentation. For example,the detectors can be used to detect light in many applicationsincluding, but not limited to, luminescence, chemiluminescence,fluorescence, phosphorescence, Raman spectroscopy, bioluminescence,environmental analysis, gene chip scanning (or bar code scanning),radiation counters, surface inspection, e.g., laser scanning surfaceinspection, flow cytometry, astronomical instrumentation, industrialequipment and materials inspection and other applications. Referring toFIG. 16, a device for optical emission spectroscopy (OES) is shown. Aschemical species are atomized and/or ionized, the outermost electronsmay undergo transitions which may emit light (potentially includingnon-visible light). For example, when an electron of an atom is in anexcited state, the electron may emit energy in the form of light as itdecays to a lower energy state. Suitable wavelengths for monitoringoptical emission from excited atoms and ions will be readily selected bythe person of ordinary skill in the art, given the benefit of thisdisclosure. The exact wavelength of optical emission may be red-shiftedor blue-shifted depending on the state of the species, e.g. atom, ion,etc., and depending on the difference in energy levels of the decayingelectron transition, as known in the art. The OES device 1600 includes ahousing 1605, a sample introduction device 1610 (or sample chamber wherea sample resides), an atomization device 1620, e.g., a flame, plasma,arc or other devices (which can produce atoms, ions or both), and adetector 1630. The sample introduction device 1610 (or chamber) may varydepending on the nature of the sample. In certain examples, the sampleintroduction device 1610 may be a nebulizer that is configured toaerosolize liquid sample for introduction into the atomization device1620. In other examples, the sample introduction device 1610 may be aninjector configured to receive sample that may be directly injected orintroduced into the atomization device 1620. Other suitable devices andmethods for introducing samples will be readily selected by the personof ordinary skill in the art, given the benefit of this disclosure. Thedetector 1630 may take numerous forms and may be any suitable devicethat may detect optical emissions, such as optical emission 1625. Forexample, the detection device 1630 may include suitable optics, such aslenses, mirrors, prisms, windows, band-pass filters, etc. The detectiondevice 1630 may also include gratings, such as echelle gratings, toprovide a multi-channel OES device. Gratings such as echelle gratingsmay allow for simultaneous detection of multiple emission wavelengths.The gratings may be positioned within a monochromator or other suitabledevice for selection of one or more particular wavelengths to monitor.Within the detector 1630, a photocathode, anode and a plurality ofdynodes can be present as described herein in reference to FIGS. 1-12,for example. The unique ability of the detectors described herein toterminate signal amplification at a saturated dynode permits operationof the detector 1630 without having to alter the entry slit widthbetween different samples. For example, in a typical instrument for OES,the entry and exit slit width may be changed to optimize thesignal-to-noise ratio for a particular sample without overloading thedetector. The photocathode of the detector would commonly be opticallycoupled to the exit slit of the monochromator. Where one or more of thedetectors described herein are used, the exit slit (and the entranceslit if desired) can be fixed, e.g., at a maximum opening, to permit amaximum amount of light to enter the monochromator. If saturation occursat certain dynodes because of excessive light, then signal amplificationcan be terminated at a saturated dynode (or downstream of the saturateddynode). The input currents for non-saturated dynodes can then be usedto determine a mean input current signal representative of the lightemission. For quantitative measurements, conventional standard curvesmay be performed to determine an accurate amount of the sample. In otherexamples, the OES device 1600 may be configured to implement Fouriertransforms to provide simultaneous detection of multiple emissionwavelengths. The detection device may be configured to monitor emissionwavelengths over a large wavelength range including, but not limited to,ultraviolet, visible, near and far infrared, etc. The OES device 1600may further include suitable electronics such as a processor 1640 and/orcomputer and suitable circuitry to provide a desired signal and/or fordata acquisition or display. Suitable additional devices and circuitryare known in the art and may be found, for example, on commerciallyavailable OES devices such as Optima 2100DV series and Optima 5000 DVseries OES devices commercially available from PerkinElmer HealthSciences, Inc. The OES device 1600 may further include autosamplers,such as AS90 and AS93 autosamplers commercially available fromPerkinElmer Health Sciences, Inc. or similar devices available fromother suppliers.

In accordance with certain examples, a device for fluorescencespectroscopy (FLS), phosphorescence spectroscopy (PHS) or Ramanspectroscopy is shown in FIG. 17. Device 1700 includes a light source1710, a sample chamber 1720, and a detector 1730. The detector 1730 maybe any one or more of the detectors described herein, e.g., a detectorcomprising dynodes coupled to respective electrometers. The detector1730 may be positioned about ninety degrees from incident light 1712from the light source 1710 to minimize the amount of light from thelight source 1710 that arrives at the detector 1730. Fluorescence,phosphorescence and Raman emissions may occur in 360 degrees so thepositioning of the detector 1730 to collect light emissions is notcritical. An optical chopper 1715 may be used where it is advantageousto pulse the light source 1710. Where the light source is a pulsedlaser, the chopper 1715 may be omitted. The light source 1710 excitesone or more electrons into an excited state, e.g., into an excitedsinglet state, and the excited atom may emit photons as it decays backto a ground state. Where the excited atom decays from an excited singletstate to the ground state with resultant emission of light, fluorescenceemission is said to occur, and the maximum emission signal is typicallyred-shifted when compared to the wavelength of the excitation source.Where the excited atom decays from an excited triplet state to theground state with resultant emission of light, phosphorescence emissionis said to occur, and the maximum emission wavelength of phosphorescenceis typically red-shifted when compared to the fluorescence maximumemission wavelength. For Raman spectroscopy, scattered radiation may bemonitored, and the Stokes or anti-Stokes lines may be monitored toprovide detection of the sample. The emission signal may be collectedusing the detector 1730, which may be, for example, a monochromator withsuitable optics such as prisms, echelle gratings and the like, that isoptically coupled to a device comprising dynodes electrically coupled torespective electrometers (or other structures, including surfaces thatcan emit secondary electrons, that is coupled to an electrometer). Whereone or more of the detectors described herein are used, the exit slit(and the entrance slit if desired) can be fixed, e.g., at a maximumopening, to permit a maximum amount of light to enter the monochromator.If saturation occurs at certain dynodes because of excessive light, thensignal amplification can be terminated at a saturated dynode (ordownstream of the saturated dynode). The input currents fornon-saturated dynodes can then be used to determine a mean input currentsignal representative of the emission. For quantitative measurements,conventional standard curves may be performed to determine an accurateamount of the sample. The device 1700 may further include suitableelectronics such as a processor 1740 and/or computer and suitablecircuitry to provide a desired signal and/or for data acquisition ordisplay or to calculate the mean input currents from the various dynodemeasurements.

In certain embodiments where fluorescence measurements are performed,the light source can be positioned below a sample tray, e.g., amicrotiter or microwell tray, that comprises samples which can beexcited and may emit light. Each well or tray can be optically coupledto a respective channel comprising dynodes and electrometers to permithigh throughput signal measurements from all wells (or selected wells)at the same time. For example, a detector array can be provided whereeach member of an array can be separately optically coupled to anindividual well, e.g., each array member can include dynodes andrespective electrometers than can function independently of other arraymembers comprising dynodes and respective electrometers. The arraymember can receive light and amplify the signal as described herein. Thedetector can be configured such that each member of the array operatesindependently of the other members. For example, one member of the arraymay measure large light signals causing termination of the signal atdynode 8 of a 20 dynode detector. Another member of the array maymeasure smaller light signals such that signal amplification is notterminated until dynode 18 of the 20 dynode detector. The gain ofseparate array members may be substantially equal to facilitate simplerdesign, and the electrometers, amplifiers and/or signal processors ofeach array member can be monitored and used to calculate a mean inputsignal for each array member and hence each sample well of the microwellplate.

In certain examples, the detectors described herein can be used inmicroscopes or other devices that receive light and permit viewing of anobject under the device. For example, one or more of the detectorsdescribed herein can be used in confocal microscopy devices. Forexample, fluorescence emission from a sample can be directed through anaperture positioned near the image plane to exclude light fromfluorescent structures located away from an objective focal plane of themicroscope. This positioning reduces the amount of light available forimage formation and provides low light levels. Signal amplification ofthe low light levels can be performed to provide an image. The fastresponse times and high sensitivities of the detectors described hereinpermit their use in microscopy applications. The detector can be locatedin a scan head of the microscope or an external housing. As describedherein, the voltage can be operated at a maximum dynode voltage toprovide a maximum gain. Offset values can also be used to adjustsensitivity if desired. For example, offset can be used to provide apositive or negative voltage to the output signal, and can be adjustedso that the lowest signals are near the detector threshold. In otherexamples, the offset can be omitted and input currents within a desiredwindow, e.g., within a window between a noise level and a saturationlevel, can be used in image construction. After the signal has beenprocessed by an analog-to-digital converter, it can be stored in a framebuffer and displayed in a series of gray levels ranging from black (nosignal) to white (saturation). The increased dynamic range provided bythe detectors described herein can permit display of more than aconventional number of gray levels. For example, in a typical confocalmicroscope with a photomultiplier, the photomultiplier has a dynamicrange of 10 or 12 bits and is capable of displaying 1024 or 4096 graylevels, respectively. Accompanying image files also have the same numberof gray levels. By using a detector with increased dynamic range, morecontrast may be achieved if desired. If desired, the microscope caninclude more than a single detector, e.g., may include three detectorswith one for a red channel, one for a green channel and one for a bluechannel, and the resulting images can be merged into a single image toprovide a representation of the actual color of the specimen under themicroscope.

Referring to FIG. 18, a schematic of a confocal microscope is shown. Themicroscope 1800 comprises components 1810 and 1820 that providepinholes, which are generally equidistant from a specimen to be imaged.Light from a light source 1805 passes through the pinhole in component1820 and is split by a beam splitter 1825. The light source 1805 can beany suitable light source including arc lamps, lasers or other lightsources commonly used in microscopy and spectroscopy. The beam splitter1825 reflects light to an objective 1830 and a specimen 1835, which isshown as a horizontal line for illustration purposes. The properties ofthe beam splitter 1825 are typically selected so that light emitted fromthe specimen (which typically has a wavelength higher than thewavelength of light from the light source 1805) can pass through thebeam splitter 1825 and to the component 1810 with the second pinhole.Light passes through the pinhole in component 1810 and is provided tothe detector 1840, which may be any one or more of the detectorsdescribed herein, e.g., a detector comprising dynodes any one or more ofwhich is electrically coupled to a respective electrometer. The passingof the light through pinhole of the component 1810 provides light to thedetector 1840 in a narrow focal plane. It will be recognized by theperson of ordinary skill in the art, given the benefit of thisdisclosure, that other components may be substituted into the device ofFIG. 18. For example, an acousto-optical device or other optical elementcan replace the beam splitter. The microscope may also include suitablelenses, gratings or other optical elements. In some embodiments, themicroscope can be configured as a laser scanning confocal microscope.

In certain embodiments, the detectors described herein can be used in acamera to provide an image, e.g., a digital image or an X-ray image,that can be displayed or stored in memory of the camera. In someembodiments, the camera may be configured as a scintillation camera todetect gamma radiation emitting from radioisotopes. Scintillationcameras are commonly used, for example, in medical imaging to viewimages after a contrast agent comprising one or more radionuclides hasbeen introduced into a subject, e.g., a human or non-human mammal, or astructure. The gamma camera generally comprises one or more crystalplanes optically coupled to an array of detectors, e.g., a crystal planeoptically coupled to 6 detectors (or other number of detectors). In someexamples, one or more of the detectors of the array may comprise any oneof the detectors described herein, e.g., a detector comprising dynodeselectrically coupled to respective electrometers. The crystal/detectorassembly is typically positioned in a scan head that can be moved overor around the object to receive gamma emissions through a gantry, arm orother positioning means, e.g., an arm coupled to one or more motors. Aprocessor, e.g., one present in a computer system, functions to controlthe position and movement of the scan head and can receive inputcurrents, calculate a mean input current and use such calculated valuesto construct and/or store images representative of the received gammaemissions. The positioning of the detectors can provide spatialresolution as each detector is positioned at a different angle relativeto incident emission. As such, saturation of any one detector may occurwith other detectors remaining unsaturated or becoming saturated at adifferent dynode. If desired, the processor can determine whether or nota dynode is saturated at any one detector and then subsequently shortother non-saturated dynodes of other detectors at the same dynode. Forexample, if detector 1 of a six detector array is saturated at dynode12, then signal amplification at other detectors can be terminated atdynode 12 to provide relative input currents, which can be used toprovide spatial resolution and/or enhanced contrast for the images. Byterminating the signal amplification at the same dynodes of differentdetectors, the use of weighting factors can be omitted and images can beconstructed in a simpler manner. Alternatively, weighting factors can beapplied based on where saturation occurs at each detector to reconstructan image. For illustration purposes, one example of a scintillation orgamma camera is shown in FIG. 19. The camera 1900 includes a collimator1910, e.g., a lead sheet collimator, optically coupled to a scintillatorcrystal 1920. Two detectors 1930 and 1940 are shown as being opticallycoupled to the scintillation crystal 1920. Each of the detectors 1930,1940 may be configured as described herein, e.g., may include dynodeselectrically coupled to respective electrometers. If desired, thedetectors 1930, 1940 may be configured to be the same or may bedifferent. The detectors 1930, 1940 are each electrically coupled to aprocessor (not shown) that can receive signals from the detectors foruse in constructing an image. The camera 1900 can be used to create 2Dimages, can be used in SPECT (single photon emission computedtomography) imaging, PET (positron emission tomography) imaging or otherimaging systems where one or more materials emits photons.

In some instances, the detectors described herein can be used insatellite instrumentation. For example, meteorological satellites,surveillance satellites or other satellites that can provide images ofthe earth (or structures, weather systems or other devices on the earth)can include one or more of the detectors described herein. In someembodiments, a satellite may include one or more of the detectorsdescribed herein and suitable circuitry or components to capture imagesrepresentative of the light received by the detectors. The capturedimages can be stored in memory and/or transmitted to a remote site byway of radio waves or other waves sent from a transmitter on thesatellite to a receiver at a remote location.

In some embodiments, the detectors described herein can be used in atelescope. For example, a refracting telescope can include a detectoroptically coupled to the objective lens and any focusing lens of thetelescope. The detector (or detector array) can include dynodeselectrically coupled to respective electrometers to measure lightsignals received by the objective lens of the telescope. The detectormay be electrically coupled to a computer system to store images or maybe wirelessly coupled to a remote computer system, e.g., in the casewhere the telescope is positioned on a satellite or otherwise isorbiting the earth, to receive the images.

In certain embodiments, certain components of the detectors describedherein can be used in a microchannel plate to amplify a signal. Themicrochannel plate functions similar to the dynode stages of thedetectors described herein except the many separate channels which arepresent provide spatial resolution in addition to amplification. Theexact configuration of the microchannel plate can vary, and in someexamples, the microchannel plate (MCP) can take the form of a ChevronMCP, a Z stack MCP or other suitable MCPs. Illustrative MCPs aredescribed in more detail below.

In certain embodiments and referring to FIG. 20A, a schematic of amicrochannel plate 2000 is shown comprising a plurality of electronmultiplier channels 2010 oriented parallel to each other. The exactnumber of channels in the plate 2000 can vary, e.g., 100-200 or more.The MCP can include electrodes 2020 and 2030 on each surface of theplate to provide a bias voltage from one side to the other to side ofthe plate. The walls of each of the channels 2010 can include a materialwhich can emit secondary electrons that can be amplified down thechannel. Each channel (or a selected number of channels) can beelectrically coupled to a respective electrometer to measure the inputcurrent from each channel. For example, non-saturated channels can beused to construct an image and saturated channels can be shorted out toprotect the channel or otherwise not used to provide an image. Ifdesired, the electrodes 2020 and 2030 can be configured as an electrodearray with an electrode corresponding to each channel to permitindependent control of the voltage provided to each channel. Inaddition, in some configurations each channel can be electricallyisolated from other channels to provide a plurality of continuous butseparate dynodes in the plate An external voltage divider can be used toapply a bias voltage to accelerate electrons from one side of the deviceto the other. In certain embodiments, the MCP's can be configured as achevron (v-like shape) MCP. In one configuration, a chevron MCP includestwo microchannel plates where the channels are rotated about ninetydegrees from each other. Each channel of the chevron MCP can beelectrically coupled to a respective electrometer or a selected numberof channels can be electrically coupled to an electrometer. In otherembodiments, the MCP can be configured as a Z stack MCP, with threemicrochannel plate aligned in a shape that resembles a Z. The Z stackMCP may have increased gain compared to a single MCP.

In some instances, a plurality of microchannel plates may be stacked andconfigured such that each plate functions similar to a dynode. Oneillustration is shown in FIG. 20B where plates 2060, 2062, 2064, 2066and 2068 are stacked together. While not shown, one, two, three, four orall five of the plates may be electrically coupled to a respectiveelectrometer. The voltages applied to each plate may be controlled usingcircuits and configurations similar to those described in referenceherein to the dynodes. In some instances, stacked MCPs can be used as,or in, X-ray detectors, and by controlling the voltage applied toindividual plates, the gain of the detector can be automaticallyadjusted for each image to provide more clear images.

In certain examples, the detectors described herein can be used in X-raydetectors such as those used to image humans or used to image inanimateobjects, e.g., to image baggage at screening centers. In particular, oneor more detectors can be optically coupled to a scintillator plate orcrystal that resides underneath baggage and can receive X-rays from anX-ray source over the baggage to image items within baggage. Similar toX-ray detectors, the detectors described herein can be used inapplications such as neutron activated techniques, which are used, forexample, in explosives detection.

In certain embodiments, the detectors described herein may be used inimage intensification devices such as those commonly present in nightvision devices. For example, the detectors described herein can beoptically coupled to a phosphor screen to amplify light, e.g., infraredlight, received by a photocathode, and provide the amplified signal tothe phosphor screen to recreate an image. For illustration purposes, thecomponents of an exemplary image intensifier are shown in FIG. 21. Theintensifier 2100 comprises a lens 2110 optically coupled to aphotocathode 2120. The photocathode 2120 receives light from the lens2110 and converts the light into electrons, which are provided to thedetector 2130. As described herein, the detector 2130 can include aplurality of dynodes where one or more dynodes are electrically coupledto an electrometer. If desired, a detector array can be present toprovide spatial resolution. In some embodiments, the detector 2130 caninclude a microchannel plate comprising electrometers electricallycoupled to respective channels to amplify the light. If saturation at aparticular channel is detected, the voltage for the particular channelmay be controlled so that the signal from that channel is terminated anddoes not overload the phosphor screen 2140. The amplified signals areprovided from the detector 2130 in the form of electrons, which strikethe phosphor screen 2140. The provided electrons are incident on thephosphor screen in the same general position in which they arrive at thedetector 2130. The incident electrons cause excitation and emission ofthe phosphors of the phosphor screen to recreate the light image thatwas incident on the lens 2110. The device 2100 can include a processorand suitable circuitry to monitor incident light signals and ensure thedetector 2130 does not become saturated. The processor can also be usedto provide an image to a display. In some examples, an ocular lens maybe present to magnify and/or focus any image for viewing by a user.

In certain configurations, the circuits and components described hereincan be used with a continuous optical detector. For example andreferring to FIG. 22, a continuous electron optical detector 2200 isshown that comprises surfaces 2230-2237. Surface 2230 is the firstsurface that can receive incident light and provide ejected electrons tosurface 2234. Surface 2234 provides ejected electrons to surface 2232(or 2231). This amplification can continue using the other surfaces.Each surface can be electrically coupled to a respective electrometersimilar to the dynode/electrometer pairs described herein. Signals fromeach surface may also be electrically isolated from signals from othersurfaces. Where saturation is detected at a surface, the surface can beshorted out to protect downstream surfaces of the detector 2200. Signalsfrom the various surfaces can be used to calculate currents, e.g., inputcurrent or output currents.

In certain embodiments, the detectors described herein can be configuredto simultaneously detect an input current signal at each dynode of aplurality of dynodes of a photomultiplier configured to receive photons,and average the detected input current signals at each dynode thatcomprises a measured current input signal above a noise current inputsignal and below a saturation current input signal to determine a meaninput current. In other embodiments, the detector can terminate signalamplification at a dynode where a saturation current is measured. Insome examples, the detector can alter the voltage at a downstream dynodeadjacent to the dynode where the saturation current is measured toterminate the signal amplification. In certain instances, the detectorcan determine the mean input current by calculating the input currentsat all dynodes and discarding calculated input currents below the noisecurrent input signal and above the saturation current input signal,scaling each non-discarded calculated input current by its respectivegain, and averaging the scaled input currents to determine the meaninput current. In some embodiments, the detector can measure the photonswithout adjusting the gain. In further embodiments, the detector canmeasure optical emission from a plurality of samples comprisingdifferent concentrations without adjusting the gain of thephotomultiplier. In other embodiments, the detector can measure opticalemission from a plurality of samples comprising different concentrationswithout adjusting entry slit width of the photomultiplier. In someinstances, the detector can calculate sample concentration from thedetermined mean input current.

In certain examples, the detectors described herein can simultaneouslydetect an input current signal of at least two internal dynodes of aphotomultiplier configured to receive photons, and average the detectedinput current signals at each of the at least two internal dynodescomprising a measured current input signal above a noise current inputsignal and below a saturation current input signal to determine a meaninput current. In other examples, the detector can terminate signalamplification at a dynode where a saturation current is measured. Insome embodiments, the detector can comprise simultaneously detecting aninput current signal at every other internal dynode of the plurality ofdynodes. In some examples, simultaneously detecting an input currentsignal at every third internal dynode of the plurality of dynodes. Incertain embodiments, the detector can comprise terminating signalamplification at a dynode where a saturation current is measured. Infurther embodiments, the detector can comprise providing a floatingvoltage at each detected dynode of the plurality of dynodes. In someinstances, the detector can comprise controlling the voltage at eachdynode independently of voltage at the other dynodes of the plurality ofdynodes. In certain embodiments, the detector can measure opticalemission from a plurality of samples comprising different concentrationswithout adjusting the gain of the photomultiplier. In other embodiments,the detector can measure optical emission from a plurality of samplescomprising different concentrations without adjusting entry slit widthof the photomultiplier. The detector can also calculate sampleconcentration from the determined mean input current. In some instances,the detector can determine the mean input current by calculating theinput currents at selected dynodes and discarding calculated inputcurrents below the noise current input signal and above the saturationcurrent input signal, and scaling each non-discarded calculated inputcurrent by its respective gain and averaging the scaled input currentsto determine the mean input current.

In some embodiments, the detectors described herein can separatelycontrol a bias voltage in each dynode of an optical detector comprisinga photocathode, an anode and a plurality of dynodes between thephotocathode and the anode to measure the photons. In other embodiments,the separately controlling the bias voltage in each dynode comprisesregulating the dynode voltage to be substantially constant withincreasing electron current. In some instances, the detector cancalculate input currents at selected dynodes of the plurality ofdynodes, discard calculated input currents below a noise current inputlevel and above the saturation current input level, scale eachnon-discarded calculated input current by its respective gain, andaverage the scaled input currents to determine a mean input current.

In certain embodiments, the detectors described herein can amplify alight signal from the sample by independently measuring an input currentat each of a plurality of dynodes in an optical detector comprising aphotocathode, an anode and the plurality of dynodes between thephotocathode and the anode. In some examples, the detector can calculateinput currents at each dynode of the plurality of dynodes, discardcalculated input currents below a noise current input level and abovethe saturation current input level, scale each non-discarded calculatedinput current by its respective gain, and averaging the scaled inputcurrents to determine a mean input current.

In some embodiments, the detectors described herein can amplify a lightsignal from the sample by independently measuring an input current attwo or more of a plurality of dynodes in an optical detector comprisinga photocathode, an anode and the plurality of dynodes between thephotocathode and the anode. In certain instances, the detector cancalculate input currents at each of the two or more dynodes of theplurality of dynodes, discard calculated input currents below a noisecurrent input level and above the saturation current input level, scaleeach non-discarded calculated input current by its respective gain, andaverage the scaled input currents to determine a mean input current. Incertain examples, the detectors can measure input currents from everyother dynode of the plurality of dynodes.

In certain embodiments, the detectors described herein may be part of asystem comprising a photocathode, an anode, a plurality of dynodesbetween the photocathode and the anode, at least one electrometerelectrically coupled to one of the plurality of dynodes and a processorelectrically coupled to the at least one electrometer, the processorconfigured to determine a mean input current from input currentmeasurements measured by the electrometer. In some embodiments, theprocessor can be configured to determine the mean input current bycalculating input currents at the at least one dynode of the pluralityof dynodes, discard calculated input currents below a noise currentinput level and above the saturation current input level, scale eachnon-discarded calculated input current by its respective gain, andaverage the scaled input currents to determine a mean input current. Ifdesired, the system can include a second electrometer electricallycoupled to a dynode other than the dynode electrically coupled to theelectrometer. In other configurations, each of the plurality of dynodesis electrically coupled to a respective electrometer. In someembodiments, the processor is configured to determine the mean inputcurrent by calculating input currents at the dynode electrically coupledto the electrometer and at the dynode electrically coupled to the secondelectrometer, discarding calculated input currents below a noise currentinput level and above the saturation current input level, scaling eachnon-discarded calculated input current by its respective gain, andaveraging the scaled input currents to determine a mean input current.In other embodiments, the processor is configured to determine the meaninput current by calculating input currents at each dynode of theplurality of dynodes, discarding calculated input currents below a noisecurrent input level and above the saturation current input level,scaling each non-discarded calculated input current by its respectivegain, and averaging the scaled input currents to determine a mean inputcurrent.

In certain embodiments, the detectors described herein, and theirmethods of using them can be implemented using a computer or otherdevice that includes a processor. The computer system typically includesat least one processor electrically coupled with one or more memoryunits to receive signals from the electrometers. The computer system maybe, for example, a general-purpose computer such as those based on Unix,Intel PENTIUM-type processor, Motorola PowerPC, Sun UltraSPARC,Hewlett-Packard PA-RISC processors, or any other type of processor. Oneor more of any type computer system may be used according to variousembodiments of the technology. Further, the system may be located on asingle computer or may be distributed among a plurality of computersattached by a communications network. A general-purpose computer systemmay be configured, for example, to perform any of the describedfunctions including but not limited to: dynode voltage control,measurement of current inputs (or outputs), calculation of a mean inputcurrent, image generation or the like. It should be appreciated that thesystem may perform other functions, including network communication, andthe technology is not limited to having any particular function or setof functions.

Various aspects of the detectors and methods may be implemented asspecialized software executing in a general-purpose computer system. Thecomputer system may include a processor connected to one or more memorydevices, such as a disk drive, memory, or other device for storing data.Memory is typically used for storing programs and data during operationof the computer system. Components of the computer system may be coupledby an interconnection device, which may include one or more buses (e.g.,between components that are integrated within a same machine) and/or anetwork (e.g., between components that reside on separate discretemachines). The interconnection device provides for communications (e.g.,signals, data, instructions) to be exchanged between components of thesystem. The computer system typically is electrically coupled to a powersource and/or the dynodes (or channels) such that electrical signals maybe provided to and from the power source and/or dynodes (or channels) toprovide desired signal amplification. The computer system may alsoinclude one or more input devices, for example, a keyboard, mouse,trackball, microphone, touch screen, manual switch (e.g., overrideswitch) and one or more output devices, for example, a printing device,display screen, speaker. In addition, the computer system may containone or more interfaces that connect the computer system to acommunication network (in addition or as an alternative to theinterconnection device). The computer system may also include one moresingle processors, e.g., digital signal processors, which can be presenton a printed circuit board or may be present on a separate board ordevice that is electrically coupled to the printed circuit board througha suitable interface, e.g., a serial ATA interface, ISA interface, PCIinterface or the like.

In certain embodiments, the storage system of the computer typicallyincludes a computer readable and writeable nonvolatile recording mediumin which signals are stored that define a program to be executed by theprocessor or information stored on or in the medium to be processed bythe program. For example, dynode bias voltages for a particular routine,method or technique may be stored on the medium. The medium may, forexample, be a disk or flash memory. Typically, in operation, theprocessor causes data to be read from the nonvolatile recording mediuminto another memory that allows for faster access to the information bythe processor than does the medium. This memory is typically a volatile,random access memory such as a dynamic random access memory (DRAM) orstatic memory (SRAM). It may be located in the storage system or in thememory system. The processor generally manipulates the data within theintegrated circuit memory and then copies the data to the medium afterprocessing is completed. A variety of mechanisms are known for managingdata movement between the medium and the integrated circuit memoryelement and the technology is not limited thereto. The technology isalso not limited to a particular memory system or storage system.

In certain embodiments, the computer system may also includespecially-programmed, special-purpose hardware, for example, anapplication-specific integrated circuit (ASIC) or a field programmablegate array (FPGA). Aspects of the technology may be implemented insoftware, hardware or firmware, or any combination thereof. Further,such methods, acts, systems, system elements and components thereof maybe implemented as part of the computer system described above or as anindependent component. Although a computer system is described by way ofexample as one type of computer system upon which various aspects of thetechnology may be practiced, it should be appreciated that aspects arenot limited to being implemented on the described computer system.Various aspects may be practiced on one or more computers having adifferent architecture or components. The computer system may be ageneral-purpose computer system that is programmable using a high-levelcomputer programming language. The computer system may be alsoimplemented using specially programmed, special purpose hardware. In thecomputer system, the processor is typically a commercially availableprocessor such as the well-known Pentium class processor available fromthe Intel Corporation. Many other processors are available. Such aprocessor usually executes an operating system which may be, forexample, the Windows 95, Windows 98, Windows NT, Windows 2000 (WindowsME), Windows XP, Windows Vista, Windows 7 or Windows 8 operating systemsavailable from the Microsoft Corporation, MAC OS X, e.g., Snow Leopard,Lion, Mountain Lion or other versions available from Apple, the Solarisoperating system available from Sun Microsystems, or UNIX or Linuxoperating systems available from various sources. Many other operatingsystems may be used, and in certain embodiments a simple set of commandsor instructions may function as the operating system.

In certain examples, the processor and operating system may togetherdefine a computer platform for which application programs in high-levelprogramming languages may be written. It should be understood that thetechnology is not limited to a particular computer system platform,processor, operating system, or network. Also, it should be apparent tothose skilled in the art, given the benefit of this disclosure, that thepresent technology is not limited to a specific programming language orcomputer system. Further, it should be appreciated that otherappropriate programming languages and other appropriate computer systemscould also be used. In certain examples, the hardware or software isconfigured to implement cognitive architecture, neural networks or othersuitable implementations. If desired, one or more portions of thecomputer system may be distributed across one or more computer systemscoupled to a communications network. These computer systems also may begeneral-purpose computer systems. For example, various aspects may bedistributed among one or more computer systems configured to provide aservice (e.g., servers) to one or more client computers, or to performan overall task as part of a distributed system. For example, variousaspects may be performed on a client-server or multi-tier system thatincludes components distributed among one or more server systems thatperform various functions according to various embodiments. Thesecomponents may be executable, intermediate (e.g., IL) or interpreted(e.g., Java) code which communicate over a communication network (e.g.,the Internet) using a communication protocol (e.g., TCP/IP). It shouldalso be appreciated that the technology is not limited to executing onany particular system or group of systems. Also, it should beappreciated that the technology is not limited to any particulardistributed architecture, network, or communication protocol.

In some instances, various embodiments may be programmed using anobject-oriented programming language, such as SmallTalk, Basic, Java,C++, Ada, or C# (C-Sharp). Other object-oriented programming languagesmay also be used. Alternatively, functional, scripting, and/or logicalprogramming languages may be used. Various configurations may beimplemented in a non-programmed environment (e.g., documents created inHTML, XML or other format that, when viewed in a window of a browserprogram, render aspects of a graphical-user interface (GUI) or performother functions). Certain configurations may be implemented asprogrammed or non-programmed elements, or any combination thereof.

When introducing elements of the aspects, embodiments and examplesdisclosed herein, the articles “a,” “an,” “the” and “said” are intendedto mean that there are one or more of the elements. The terms“comprising,” “including” and “having” are intended to be open-ended andmean that there may be additional elements other than the listedelements. It will be recognized by the person of ordinary skill in theart, given the benefit of this disclosure, that various components ofthe examples can be interchanged or substituted with various componentsin other examples.

Although certain aspects, examples and embodiments have been describedabove, it will be recognized by the person of ordinary skill in the art,given the benefit of this disclosure, that additions, substitutions,modifications, and alterations of the disclosed illustrative aspects,examples and embodiments are possible.

The invention claimed is:
 1. An optical detector comprising aphotocathode configured to receive photons, an anode and a plurality ofdynodes between the photocathode and the anode, in which each of theplurality of dynodes is configured to amplify an electron signalrepresentative of the photons received by the photocathode, wherein atleast two of the plurality of dynodes are electrically coupled to arespective electrometer, wherein the optical detector further comprisesa processor configured to detect a signal from each respectiveelectrometer and terminate signal amplification at a saturated dynodeupstream of the anode.
 2. The optical detector of claim 1, in which theplurality of dynodes and the respective electrometers are in a samehousing.
 3. The optical detector of claim 1, in which each respectiveelectrometer is electrically coupled to a respective signal converter.4. The optical detector of claim 3, in which each of the respectivesignal converters is an analog-to-digital converter.
 5. The opticaldetector of claim 4, in which each of the analog-to-digital convertersis electrically coupled to the processor, in which eachanalog-to-digital converter is electrically isolated from otheranalog-to-digital converters.
 6. The optical detector of claim 4,further comprising a respective power converter electrically coupled toeach respective electrometer and analog-to-digital converter pair. 7.The optical detector of claim 1, wherein the processor is electricallycoupled to each of the plurality of dynodes and is configured to preventa current overload at at least one dynode of the plurality of dynodes.8. The optical detector of claim 7, in which the processor is configuredto alter the voltage at, upstream or downstream of at least one dynodewhere a saturation current is detected.
 9. The optical detector of claim8, in which the processor is configured to invert the polarity of avoltage at, upstream or downstream of the at least one dynode where thesaturation current is detected.
 10. The optical detector of claim 7, inwhich the processor is configured to prevent any substantial secondaryelectron emission from at least one dynode downstream of the at leastone dynode where the saturation current is detected.
 11. The opticaldetector of claim 1, wherein every other dynode of the plurality ofdynodes is electrically coupled to a respective electrometer.
 12. Theoptical detector of claim 11, in which the plurality of dynodes and therespective electrometers are in a same housing.
 13. The optical detectorof claim 11, in which each respective electrometer is electricallycoupled to a respective signal converter.
 14. The optical detector ofclaim 13, in which each of the respective signal converters is ananalog-to-digital converter.
 15. The optical detector of claim 14, inwhich each of the analog-to-digital converters is electrically coupledto the processor, in which each analog-to-digital converter iselectrically isolated from other analog-to-digital converters.
 16. Theoptical detector of claim 14, further comprising a respective powerconverter electrically coupled to each respective electrometer andanalog-to-digital converter pair.
 17. The optical detector of claim 1,wherein every third dynode of the plurality of dynodes is electricallycoupled to a respective electrometer.
 18. The optical detector of claim1, wherein every fourth dynode of the plurality of dynodes iselectrically coupled to a respective electrometer.
 19. The opticaldetector of claim 1, wherein every fifth dynode of the plurality ofdynodes is electrically coupled to a respective electrometer.
 20. Theoptical detector of claim 1, wherein a dynode in the middle of theplurality of dynodes is electrically coupled to a first electrometer,and wherein a dynode downstream from the dynode in the middle of theplurality of dynodes is electrically coupled to a second electrometer.